To compensate for slump loss during transportation, extra water is typically added to concrete at the plant or at the site to increase slump. Verifi enables this water to be added in transit.
So, does adding water to concrete in transit increase or decrease the amount of water added to concrete? According to a recent study from Missouri University of Science & Technology (MS&T) sponsored by the Missouri Department of Transportation (MoDOT), equal or less water is used when added in transit instead of at the jobsite.
The researchers considered two scenarios using Verifi-equipped trucks. In the first scenario, Verifi was set to add water every time the slump decreased by 0.5 in below target (“In transit water addition”). In the second scenario, slump decreased over 90 minutes and water was added at the end (“Single water addition at end”). This second scenario represents conventional industry practice. All mixes started at the target slump for the mix.
Figure 28 from the report shows that equal or less water was typically added to the concrete when the water was added in transit.
Figure 29 shows that compressive strength was higher when water was added in transit (denoted “Automatic Water addition” in the chart) compared to mixes with water added at the end of the delivery. This was expected due to less water added.
(Note that the mix design should be adjusted to account for this added water–regardless of where it is added–so that the maximum water/cementitious materials ratio is not exceeded. Verifi tracks water additions and can be set to stop water additions after the maximum water content for the load is reached.)